Program switching system



l2 Sheets-Sheet 1 Aprll 23, 1940- A. E. BAcHELl-:T

PROGRAM SWITCHING SYSTEM med sept. 22, 195s toi E n uz .2G S6 S A? JU,zn E w j 4 A T TOR/VEV April 23, 1940. A. E. BACHELET PROGRAM SWITCHINGSYSTEM Filed Sept. 22, 1938 l2 Sheets-Sheet 3 TRANS- MISS/0N LOSSr PADlRE C.

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/6 Il; 4 El Tlf AT TOR/VE V April 23, 1940- A. E. BACHELET 2,198,326

PROGRAM SWITCHING SYSTEM Filed Sept. 22, 1938 12 Sheets-Sheet 4 FIG. .5

NEW YORK (cus) /NvE/VTOR AEBACHELET A TTORN-V April 23, 1940. A. E.BAcHl-:LET 2,198,326

PROGRAM SWITGHING SYSTEM med sept. zz, 195e 12 sheets-sheet s Flea " NEWYORK DIRE C Tl 0N l/V VEN TOR ,4.5. @4Q/#EL E T A TTORA/EV April 23,1940- I A. E. BACHELET 2,198,326

PROGRAM SWITCHING SYSTEM Filed Sept. 22, 1938 l2 Sheets-Sheet 6 FIG. 7

NEW YORK TTENUA TION 1 EQUAL [2ER /N VE N TOR 515A CHHET April Z3 1940-A. E. BAQHELET ZQSZ@ PROGRAM SWITCHING SYSTEM Filed Sept. 22, 1958 12Sheets-Sheet l ro Pol/vrs NaRr/-l 9/9 Fl@ 8 ALBA/vv Moo. M "E" lRECT/ONApril 23, i940. A E. BACHELET PROGRAM swITcHING SYSTEM Filed Sept. 22,1938 ALBA/vv 12 'sheets-sheet 8 DELAY EQUAL lzsn) POLAR/25o 90g /NVENTORAE. BACHELET A TTORNE'V i EQU/PMEN? April 23, 1940. A. E. BACHELETPROGRAM SWITCHING SYSTEM Filed Sept. 22, 1938 12 Sheets-Sheet 9 FIG' ,0HARTFORD uvom? COMMON glo /Nl/ENTOR ,4.58/4 CHE L E T A T TORNE V April23 1940 A. E. BACHELET 2,198,326

PROGRAM SWITCHING SYSTEM Filed Sept. 22, 1958 12 Sheets-Sheet 10 HA R TFORD /29 r/a/v Ker A TTENUA T/0N l EQUAL /ZER INVENTOR Af. BACHELET @y AT TORNE V April 23, 1940 A. E. Bini-151451'l 2,198,326

PROGRAM SWITCHNG SYSTEM Filed Sept. 22, 1958 12 Sheets-Sheet 11 DELAYEQUAL /ZEILH POLAR/ze /209 4 fn?. /2/ EM N202 f T f /N VEN TOR ,4.5.BACHELET Aprll 23, 1940. A E. BACHELET PROGRAM SWITCHING SYSTEM 12vSheets-Sheet 12 Filed Sept. 22, 1938 To Po/Nrs Non H Alva sAsr F G. /3Bos ro/v S PAD mmsmss/0N r... Il. L

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A TTOR/VEV Patented Apr. 23, 1940 UNITED STATES PATENT OFFICE PROGRAMSWITCHING SYSTEM Albert E. Bachelet, New York, N. Y., assigner to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation of`New York .This invention relates to telephone transmission systems, andmore particularly to systems for transmitting radio broadcast programsover wlres from any one of a plurality of interconnected broadcaststations to all the others and is an improvement on the system disclosedand claimed in the United States patent to Bachelet and Brand 2,110,284,issued March 8, 1938.

An object of the invention is to provide a simplified and flexibletransmission network,

employing one-Way amplifiers, for interconnecting a plurality ofbroadcast stations whereby any station may assume control of the networkn and condition all the amplers in the network 1D to transmit from thatstation to all the `other stations.

In systems of the character herein disclosed, and also as shown in theabove-referred to Bachelet et al. patent, the points in the system wheretwo or more lines are joined, i. e., connected together, are calledbridging points. At all such bridging points in the system disclosed inthe Bachelet et al patent, individual one-Way ampliers are included ineach line and so ar- 35 ranged that normally they are connected in adirection to transmit away from the bridging point over the respectivelines, but in-response to control currents received over any line, there speotive amplifier co-nnections are reversed so "U that that amplierthen transmits toward the bridging point whereas all the otheramplifiers at that point still remain in condition to transmit away fromthe bridging point.

Q A feature of the present invention resides in 'M the use of a commonamplifier at each bridging point and switching means thereat, individualto each line terminating thereat, normally connecting the respectivelines in multiple to' the output of the amplifier and adapted whenoperated by control current received over any line to connect that lineto the input of the amplifier without disturbing the connection of theother lines to the output.

Other features of the invention will appear from the followingspecification and appended claims:

Fig. 1 of which schematically represents a broadcast network withbridging points at Phila- 50 delphia, New York, Albany, Hartford andBoston.

Fig. 2 shows the manner in which the remaining Figs. 3 to 13 of thedrawings may be joined to show a more detailed arrangement of thesystem.

A detailed description of the operation of the` system now follows:

By referring to Figs. 3 to 13, when joined as shown in Fig. 2, Figs. 3and 4 represent a socalled bridging point at Philadelphia, including alocal broadcasting station, from which point an open-wire line extendsto the south and west and a cable line to New York, represented by Figs.5, 6 and '7, where another local broadcast station is located. From NewYork a cable line extends north to Albany, represented by Figs. 8 and 9,and at which point still another local broadcast station is located.From this point an open-wire line also extends to points still furthernorth and west.

From New York, an open-wire line extends eastward to Hartford,represented by Figs. l0 and 11, and from which point still anotheropenwire line extends to Boston, represented by Figs. 12 and 13. Toserve points still further east of Boston an open-Wire line is shownextending eastward from that point.`

The ampliiiers employed in the present system may be of the high level,high power, feedback type disclosed in the copending application, filedin the name of S. T. Meyers, Serial No. 216,679, filed June 30, 1938,and have an output sui-liciently great to supply a bridging network towhich may be connected, through an autotransformer, a relatively largenumber of open-wire lines or cable lines or a combination of both. Theautotransformers are indicated by reference characters 3l5, 5H, 9I3, IGMand |2I3 respectively.

The linesfare connected to taps on the autotransformers Iso chosen as toprovide'the proper level of transmission for the particular lines. Ingeneral, all open-wire lines are connected across substantially theentire winding of the transformer and the cable and studio lines areconnected across intermediate taps, as shown.

It will be assumed, for `purposes of description, that the broadcast:station at Philadelphia, shown at the bottom of Fig. 4 has had controlof the network for the purpose of transmitting a program which wasaccomplished by operating key M7, and that at the conclusion, or nearthe end, of the program, thekey 4|? was released.

The operation and subsequent releasel of key system in an operatedcondition, some of which are normally operated and others operated andlocked in an energized condition by the` operation ci the key referredto, i. e., 305, 300, dill, 003, est, elfi, 501, 000, 50|, 006i, 000,l10|, 'm3, lill), 008, 003, 550e, 05|, 8M, 905, 00, |003, |004, ||0|,litigi, i505, H00, SH2, IHS, lIIll, |20I, |202, |302, |303, Etta, itil?,|308 and |0l2. l

A circuit exists at this time from the microphone dit at Philadelphiaover the upper closed contacts ci relay 400, inner iront contacts ofrelay 305 and inner back contacts of relay 3|0 to the input of commonamplier 300. The output of ampliner 300 is connected over inner backcontacts of relay 30| and upper closed contacts of relay 20| to theopen-wire line leading to the west and south and over inner backcontacts of relay 000 and upper closed contacts of relay 4G55 to theline ft2@ leading to New York at which point line drill is connected tothe input oi common amplifier 50d over upper closed contacts of relayelle, inner iront contacts of relay ll', and inner baokcontacts of relayelli. The output of amplifier de@ Vis connected over inner back contactsof relay 59| and upper closed contacts of relay '50| to line l|2 leadingto Albany, over inner hack contacts of relay 503 and upper closedcontacts of relay 700 to line IIS leading to Hartford and over innerback contacts of relay 535 and upper closed contacts of relay 00| to theradio transmitter GIE at New York.

The line 'H2 is connected tothe input of amplifier 000 at Albany, overupper closed contacts of relay 30G, inner front contacts of relay 905and .inner back contacts of relay 0|0. The output of amplifier 000 isconnected to line 8|3 leading to the north and west over inner backcontacts of relay 003 and upper closed contacts of relay 303 and to theradio transmitter 8| 0 of the Albany broadcast station over inner backcontacts of relay 00| and upper closed contacts of relay 80|.

Line H3 supplied 'from' the output of amplifier 500 at New York isconnected to the input of amplifier |000 at Hartford over upper closedcontacts of relay H04, inner front contacts oi relay i003 and inner backcontacts of relay I0| 0.

At Hartford no broadcast station is shown and .tor purposes of thisdescription, the bridging circuit including amplifier |000 is merely anintermediate amplifying point in the line between New York and Boston.Therefore the output of ampliner |000 is only connected to one line I I|8 which extends to Boston, which includes the inner normal contacts ofrelay |00| and upper closed contacts of relay IIOI.

Line Hi8 terminates in the input of amplifier |200 at Boston afterpassing over the upper closed contacts of relay |302, inner frontcontacts of relay l20| and inner back contacts of relay |220. At Bostonthe output of amplifier |200 is connected to a line I3 I 0 extending topoints east, over inner back contacts of relay |203 andy upper closedcontacts of relay |303 and to the local broadcast station transmitter|320 over inner back contacts of relay |205 and upper closed contacts ofrelay i305.

It will also be observed thatl at Philadelphia, direction lamp 42| islighted indicating that line M0 is connected for transmission from eastto` west, lamp 222 is lighted indicating that line 420 is connected fortransmission from west to east and lamp 623 is li-ghted indicating thatthe Philadelphia studio, i. e., microphone H8 is connected for outgoingtransmission.

At New York lamps M3, 6|4,"||4 and 'H5 are lighted. At Albany lamps 820,82| and 822 are lighted. At Hartford lamps IIIO and H20 are lighted. AtBoston lamps |322, |323 and |324 are lighted, all for the same purpose,i. e., to indicate to the respective attendants in which direction thecorresponding lines are connected for transmission.

In addition to the direction lamps SI2, E III, etc., above-referred to,cue lamps and controlling relays are located at each brid-ging point asfollows: relay 3|2; at New York lamp 5H and relay 5|2; at Albany lampSII and relay SI2; at Hartford lamp |0I| and relay |0|2; and at Bostonlamp |2|| and relay |2I2. Under the condition assumed, after key H1 hasbeen released and before a corresponding key at another point has `beenoperated, all five oi these lamps will be At Philadelphia lamp 3I| andcontrolling L lighted due to the release condition of their respectivecontrolling relays. The operation of these relays and the consequentextinguishing -1 of their corresponding lamps will be referred to laterin connection with the operation of control key`I3I'I. to Boston.

The foregoing is a brief description of the conditionofthel system at orjust before the conclusion of a broadcast originating in thePhiladelphia studio which, has been arbitrarily assumed as a startingpoint for the followingk description of the operation of the switchingapparatus.

It will now be assumed that the studio of the Boston broadcastingstation represented by the microphone |32| is to originate the nextnetwork program and therefore when the Boston switching attendant,responsible for connecting the Boston station to the network notes thelighted cue llamp I2|| and is appraised, usually by a loudspeakerconnected to the circuit, that the Philadelphia broadcast is nished, heactuates key |3II which `initiates the operation of relays.

throughout the network to condition it in such a manner that the programoriginating in the Boston studio, as represented by microphone |52 I,will be transmitted into the rnetwork and be received by all thestations for broadcast from their respective transmitters.

When key |3I'I is operated it closes a circuit to operate relay I3I6 ina circuit from battery over inner normal contacts of relay |3|8, windingof relay IBIS, and normal contacts of key |325 to 5- grcund.. Relay |3|6in operating opens its inner back contacts thereby preventing relay |3|8from operating and at its inner front .contacts con-y nects battery toconductor |320 for a purpose to be later referred to. Relay |3||i inoperating also k y opens its upper back contacts thereby opening thepreviously closed circuit which held relay |305 operated which relaythereupon releases and opens its upper and lower closed contacts whichextinguishes lamp |324 and disconnects the transmitter |320 from ythenetwork. Closure of the upper front contacts of relay |3|0 operatesrelay |3|5 in an' obvious circuit. Release of relay |305 closes itslower back contacts thereby closing a circuit to operate relay |300which can be traced from battery, winding of relay |306, lower backcontacts of relay |305, upper'back contacts or relay ISIS and contactsof key |325 to ground. Operation` of relay |306 connects the microphone|32! over its upper front contacts to conductors |321 and |328 which areconnected to the inner armatures of relay |205. Operation of relay |305clos'esfits lower inner contacts thereby lighting direction lamp |029and by closing its lower middle front contacts, it completes a circuitto con- CII to Fig. 12 where it is multiplied to conductors |214 and|2|5. Conductor |2|5 can be further traced through Fig. 13 over thelower front contacts of relay |3|2 and winding of relay |3|4 to groundedcontacts of key |331. Relay |3|4 operates and opens its upper backcontacts which perform no function at this time. It also opens its innerback contacts and closes its inner front contacts thereby connectingbattery to the sirnplex circuit of line |3|0 which extends to the east.The result of connecting this battery to the line |3|0 performs nofunction under the conditions previously assumed for the reason that thenext bridging point to the east (not shown) was in condition to receivea program from the west prior to operation of key |3| 1 and hence as itis to continue to receive a program this time from Boston instead ofPhiladelphia, no change in the circuit of the next eastern bridgingpoint is necessary.

Conductor Hilft can be traced through Fig. 13 over the lower frontcontacts of relay |308 and winding of relay |3|0 to ground at contactsof key |330. Relay |3|0 operates and opens its upper back contactsthereby releasing relay |302 which has previously been energized. Relay|302 in releasing opens its upper front contacts thereby disconnectingthe attenuation equalizer |330 from the line HI8 to Hartford. Therelease of relay |302 opens its inner lower front contacts therebyextinguishing the direction lamp |322, opens its lower middle frontcontacts and closes its lowermost back contacts thereby completing acircuit to operate relay |30| which can be traced over the upper frontcontacts of relay |300 to grounded contacts of key |335.

Relay |30! in operating inserts the transmission loss pad |333 in theline Il I8 to Hartford,

lights the direction lamp |334 and also interposes a second break in theoperating circuit of relay |302, thus preventing this relay fromoperating when key |3|`| is released. Release of relay |302` opens itslower middle front contacts, the circuit energizing relays |301 and|202, which relays release. The release of relay |202 releases relay|20i which disconnects the line |||8 from the input of amplier |200 andconnects it to the outputv thereof. Conductor |330 which was connectedto ground through resistance |33| and the upper winding of relay |3|5,when relays |300 and |3i|i operated,l extends to Fig. 12 and thence tobattery through the windings of relays |200 and |200. Relay |200 ispolarized, i. e., its lower winding is continuously energized in a localcircuit in a direction tending to hold the relay in its released ornon-operate condition and due to the value of resistance |33I, thecurrent iiowing in the upper winding of relay |200 at this time isinsuiiicient to overcome the effect of the current in the lower windingand to operate the relay. Relay |200, however, is more sensitive andoperates in the circuit traced, thereby clos` ing an obvious circuit tooperate relay |205. Re-` lay |310 is, therefore, held operated inserieswith relay |200. Relay |205 in operating opens its upper and lower innerback contacts thereby disconnecting the output of the amplier |200 fromconductors |327 and |320 and connecting these conductors to the input ofthe amplifier over the `inner normal contacts of relay |2|0. It will nowbe observed that whereas before key |3|`| was operated, the input ofamplier |200 was connected to line |||8v incoming from Hartford throughthe attenuation equalizer |336, and the output of amplifier |200 wasconnected over conductors 321 and |320 and the front contacts of relay|305, through the transmission loss pad |333 to the Boston broadcasttransmitter |320. Now these circuit connections are broken down andinstead the Boston studio (microphone 32| is connected through theattenuation equalizer |330 and over the front contact of relays |300 and|205 and back contacts of relay |2|0 to the input ofthe amplifier |200and the output of the ampliiier is connected to line |||8 to Hartfordthrough the transmission loss pad |333. It will be further noted thatrelay |203 remains in its released condition and therefore the output ofamplier |200 remains connected over the inner back contacts of relay|203 and front contacts of relay |303 to the line |3|9 extendingeastward from this point, as before.

It will be recalled that when relay |3|0 operated, it connected batteryto conductor |332 forming a part of a simplex circuit on line |||0extending to Hartford, the other end of which simplex circuit passesover the inner back contacts of relay |||0 and the uper winding of relay|00 to ground at contacts of key ||2|. Connection of battery to theBoston end of this simplexcircuit by operation of relay |3|0 causesrelay |09 at Hartford to operate. Operation of relay H09 operates relayH00 which relay opens its upper back contacts thereby relasing relay H00which in turn releases relay ||0|. 'Ihe release of relay ||0|extinguishes the direction lamp l0 and closes an obvious circuit tooperate relay H02. The operation of relay H02 closes at its lower middlecontacts a circuit to hold relay H01 and to operate relay |002 which canbe traced from ground, resistance H22, upper winding and iront contactsof relay H07, lower middle front contacts of relay H02, conductor |23,winding of relay |002 and upper winding of relay |000 to battery. Due toresistance H22 the flux generated in the upper winding of relay |000 isinsufficient to overcome the bias effect of the lower winding whichtends to keep this relay released and consequently it does not operate.Operation of relay |002 operates relay |00! which disconnects the line|||8 from the output of ampliiier |000 and connects it to the inputthereof over the inner back contacts of relay |0|0. Op-

eration of relay H08 closes its lower front contacts thereby connectingbattery to conductor H24 which extends to Fig. 10 and is multiplied toconductor |0|3 which extends back to Fig. 1l where it passes over thelower back contacts of relay l5, and through relay HIT to ground atcontacts of key H25 whereupon relay il |'l op crates and opens its upperback contacts thereby releasing relay |||2 which in turn opens thepreviously closed energizing circuit for relay l |00 which releases.Relay H00 when released closes its lowerinost back contacts, and closesa circuit to operate relay H03. The release of relay H04 extinguishesdirection lamp H20 and operation of relay H03 lights the direction lampH20. The release of relay H04 also opens its lower middle contactsthereby releasing relays HM and |004. The release of relay |003 releasesrelay !003 which transfers conductors H21 and H20, which terminate theline H3 from New rcfs York, from the input of amplifier |000 to theoutput circuit thereof. It will now be noted that line |||3 from Boston,over which a program will be transmitted from that point, is nowconnected through the attenuation equalizer H29 and upper contacts ofrelay H02 to the input of amplier |000 over front contacts of relay E00!and back contacts of relay |0|0 and the output of amplifier |000 isconnected over back contacts of relay |003, upper closed contacts ofrelay M03 and through transmission loss pad H30 to the line 'H3extending to New York.

vIt will further be noted that operation of relay ill? connected batteryover its inner iront contacts to conductor ||3| forming the Hartford endof the simplexv circuit of the line 'H3 which terminates at the New Yorkend in ground at contacts of key 'liti after passing through the upperwinding of polarized relay lll). Relay 'H0 operates in this circuitthereby releasing relay 70S and operating relay '108. The release ofrelay .109 opens its upper contacts thereby releasing the previouslyoperated relay E03 which extinguishes the direction lamp llii 'andcloses its lower back contacts thereby completing a circuit to operaterelay Nit which circuit includes the upper back contacts of relay 'llland contacts of the key llt. Relay 'E03 in releasing opens its uppercontacts thereby removing the'transmission loss pad 'H8 from the linecircuit and the operation of relay |04 substitutes the attenuationequalizer 'l ll'. Operation of relay 'H04 also lights the directionlamp. 'H9 and by closing its lower middle contacts completes a circuitto hold relay '|08 operated and to operate relay 5M which can be tracedfrom ground through resistance T20, upper winding and contacts of relay'508, lower middle contacts of relay '|04 and conductor l2| to Fig. 5,where it can be further traced through the winding of relay 504 and theupper winding of relay 509 to battery. Due to the value of resistance'|29, the upper winding of relay 599 does not receive suiiicient currentto overcome the non-operate bias of the lower winding and this relayremains released. Relay 500 operates in this circuit and operates relay503. 503 in operating transfers the line H3, which now includes uppercontacts of relay 'E04 and attenuation equalizer lll from the output ofampliiier 500 to the input circuit thereof over inner normal contacts ofrelay 5|0, thereby conditioning this point to receive, amplify andretransmit to the north and west the program transmitted over the line'H3 from the east.

Returning to Fig. 7 when relay 709 released, it closed its lower backcontacts thereby connecting battery to conductor '|22 which-extends toFig. 5 where it is multipled to corresponding conductors dit, 5M and 5|5extending back to the upper portion of Fig. 7 and to Fig. 6.

Battery applied to conductor |22 can be traced over conductor 5M toconductor l23, inner upper back contacts of relay 106 and winding ofrelay lill to ground at contacts of key 3243. Relay '|707 operates andconnects battery to the simplex conductor 'F25 connected to the line M2extending to Albany. Under the condition assumed, the line 'H2 waspreviously transmitting a program in a direction from New York to Albanyand as the same condition is to prevail when the program is originatedin Boston, the connection of battery to the simplex circuit on line H2performs no useful function at this time other than to operate relaysBIS, 8|3 and 809 and Relay t0: extinguish the cue lama SH which will beYreferred to later. 'I'hel operation of relay als connects battery-to thesimplex on line 8I8 eX- tending further to the north and west, thefunction of which will be obvious from the present description involvingFigs. 3 to 13.

The battery applied to conductor 5|4 by the release of relay '|09-extends oVer conductor M5, inner back contacts of relay 606 and windingof relay 001, to ground at contacts of key Siti. Relay 601 performsV nofunction at this time other than to open its contacts thereby preventingaccidental operation of key 6H from aieoting the switching operationinitiated by the operation of key I 3=|1 at Boston.

As the New York transmitter 6H was previously receiving andretransmitting the program origina-ted at Philadelphia and is tocontinue to receive the program` from Boston, no further change isrequired in this part of the circuit.

Battery applied to conductor 5|5 by the release of relay m9. passes overthe inner back contacts of relay 09 and through the winding of relay 0|@to ground at contacts of key EES, Relay 6|0 opcrates and opens its uppercontacts thereby releasing relay 604 which in turnextinguishes thedirection lamp 6M and closes the circuit to operate relay 003. Relay 603lights the direction lamp 0&2. The release of relay 604 and theoperation of relay 003 removes the attenuation i;

equalizer 620 from the line 420 and substitutes the transmission losspad 62|. The release of relay 604 also opens its lower middle contactsthereby releasing relays 008, 508 and 507. The release of relay 501reverses the connection` between line 420 and the amplier 500, i. e., itconnects the line to the ampliiier output instead ci to the ampliiierinput, as was the condition when the program was being transmitted toand through New York from Philadelphia.

It will now be noted that the line H3 between New York and Hartfordwhich previously was connected to the output of amplifier 500 through atransmission loss pad is now connected through an attenuationequalizervto the input of rthe amplifier and the line 420 between New York andPhiladelphia which previously was connected through an attenuationequalizer to the input of amplifier 500 is now connected to the outputof the amplifier through a transmission loss pad. Hence it may` be saidthat amplier 50d at New York has been reversed with respect to lines Alland H3, but not with respect to the line to .Albany or the New Yorkbroadcast transmitter. When relay 6H) operated, it connected battery 'tothe simplex circuit of line 420 thereby causing operation of relay 4|2at Philadelphia in a circuit through relay 4i2 to ground and contacts ofkey 424. Operation of relay 4&2 closes its upper front contacts toenergize relay 4H over its lower winding and opens, at its uppe backcontacts, the energizing circuit of relay 03 which releases, therebyextinguishing the direction lamp 422 and removing the transmission losspad 425 from the line 420. The release of relay 403 also closes itslower back contacts to energize relay 404 in a circuit to ground atcontacts of key 424 over the upper back contacts of relay 4|3. Relay 404operated inserts the attention equalizer 420 in the line d20 in place oithe transmission pad 425, lights lthe direction lamp 421 and at itslower middle front contacts closes a circuit to hold relay 4|| operatedand to energize relay 304, thevcircuit of which can be traced fromground, resistance 428, upper windv ing and contacts of relay 4| lowermiddle front contacts of relay 404, conductor 420, winding of relay 304,and upper winding of relay 309 to battery. Relay 300 is polarized, inthe same `manner as relays 5013, |009, etc., previously mentioned, anddue to the value of resistance 428 does not receive sufficient currentto overcome the non-operate bias of the lower winding `and cause therelay to operate. Relay 304 operates, however, which in turn operatesrelay 303 which transfers the line 420 from the output of amplifier 300to the input thereof. Operation of relay 4| 2 connects `battery to aconductor which extends to Fig. 3 and is multipled to conductors 3|3 and3|4. Conductor 3|3 can be traced back to Fig. 4 and to ground atcontacts of 43| over the lower front contacts of relay 408 and windingof relay 4|0. `Relay 420 operates and connects battery to the simplexcircuit on line 4|9 extending to the west and south which willaccomplish such functions as may be required at the distant bridgingpoints to control the amplifier connections thereat in order that theproper direction of transmission is maintained. Connection of battery atrelay 4t2 over conductors 430 and 3I4 passes over the inner backcontacts of relay 4|5 and through relay H6 to ground at contacts of key432. Relay 4|@ operates in this circuit and at its inner back contactsopens the circuit for operating relay H5 in order that accidentaloperation of key lill at this time will not interfere with the controlnow being exercised by key |3| at Boston. Operation of relay 4|6 alsoopens its upper back contacts thereby releasing relay 406 which opensits upper contacts thereby disconnecting the Philadelphia studio asrepresented by the microphone M from conductors 433 and 434 extending toFig. 3. Release of relay 406 also extinguishes the direction lamp 423,closes its lower back contacts thereby completing a circuit to operaterelay 405 which can be traced over the upper back contactsrof relay 4I5to ground at contacts of key 432. Relay 406 in releasing also opens itslower middle front contacts thereby opening the circuit which haspreviously held relay 4M and relay 306 energized whereupon these relaysrelease. The release of relay 306 releases relay 305 which transfersconductors 433 and 434 from the input of amplifier 300 to the outputthereof. Operation of relay 405 lights the direction lamp 435 and closesits upper contacts thereby connecting the Philadelphia broadcastingtransmitter 435 to the output of amplifier 300 over the back contacts ofrelay 305 previously mentioned.

From the foregoing description it will be now seen that whereas prior tooperationof key I3I'l at Boston the network was interconnected in such amanner that transmission was from the microphone H0 at Philadelphiaoutward to the west and south and eastward to the next bridging point(New York) at which point an amplifier was interposed in the circuit andconnected in such a manner that transmission received over the line fromPhiladelphia was amplified and retransmitted to a local broadcaststation, to Albany in the north, and eastward to Hartford at which pointanother amplifier was interposed the output of which was connected to aline extending to Boston. At Boston still another amplifier was includedin the network having its input terminating the line from` Hartford andits output connected to a line extending east from that point and alsoto a local broadcast station at Boston, under the new condition, i. e.,

when key |3|`| at Boston was operated, the connections of` theamplifiers at Boston,` Hartford,A

New York and Philadelphia are such that a program originating at Bostonwill be transmitted to points east, West to Hartford where it isamplified and retransmitted to New York and at New York where it isreamplified and transmitted north to Albany, to the local New Yorkstation, and west to Philadelphia. l At Philadelphia the transmission isreceived, amplified and now supplied to the local broadcast station andalso transmitted as before to the west and south.

Located in each bridging point, usually in the control room where theamplifiers and switching equipment are located, are` other signal lamps3H, 5H, 0H, |0|| and H2M which are called cue lamps. These lamps arecontrolled by individual relays SH2, 5|2, etc., which are energizedwhenever any one of the control keys such as `l l 'L3 l, etc., isoperated and thereby extinguishing the respective lampsy which arenormally lighted in an obvious manner. For example, under the rstassumed condition, i. e., when the Philadelphia attendant released thecontrol key 4H at or near the end of the Philadelphia program, relay llwas released thereby removing battery from the conductor extending toFig. 3, `thereby releasing relay 3|2 which lighted the cue`lamp 3H.Removal of battery from this same conductor'released relay 4|3 whichremoved battery from the simplex control circuit over line 420 to NewYork thereby releasing relay 000 which removed battery from conductor5|4 and released relay |2 thereby lighting cue lamp 5| l. `arereleasedRelay ll, released, disconnected battery from the simplex `control`circuit over line 'H2 which released relay 0|5 disconnecting batteryfrom the conductors extending to Fig. 9 thereby releasing relay SH2andclosing the circuit to light cue lamp 0l l Relay` 7| l, released,disconnected battery from the simplex control circuit over the line 'H3to Hartford whereupon relay IMG released thereby releasing relay lliwhich in turn .disconnected battery from the conductors extending toFig. 10 to which relay |012 is multipled. This relay therefore releasedand lighted cue lamp |0l|. The release of relay I l5 also caused relay|0|0 to release thereby disconnecting battery from the simplex circuit`over line HI8 to Boston where it released relay |309 which operatedrelay |303 and disconnected battery from the conductor extending to Fig.12 where it is multipled to the relay I2|2 which thereuponreieasedlighting the cue lamp -|2I|. The lighting of a cue lamp at each bridgingpoint is a visual signal to the attendant that the present program is orsoon will be concluded and that the attendant at the next pointscheduled to transmit a program should be ready to seize control of. thenetwork at the proper moment. This may be at some predetermined point onthe clock regardless of whether the program being transmitted iscompletely finished or when the attendant recognizes some audible cueheard over a monitoring loud-speaker or other means.

As it has been assumed that Boston is to take control of the network andoriginate the next program, following the conclusion of the onetransmitted from Philadelphia, the Boston control room attendant watchesfor the cue lamp |2|| to light and at the proper time following thelighting of the lamp operates key lf3|1 which, as previously describe@causes a succession' of re- Relays lill and 'lll also lay operations toreconnect battery at the diierent points in the network to the multiplecon- -ductors to which relays |2|2, |0I-2, SI2, 5|2 and SI12 areconnected thereby causing these relays to operate and extinguish theirrespective cue llam-ps as an indication to all attendants `that thenetwork has been seized at some point and is `locked out of control byall other poi-nts luntil the cue lamps are again lighted by the releaseof the control key which inthe present case is key Itll at Boston.

Associated witheach amplifier 300, 500, etc., is a common transmissioncorrecting network which -may be included in whichever line istransmitting -intothe input of the particular amplifier by the operation4of its associated switching relay 3-|0, 5|0, etc. The reason for thiscommon equipment .is to avoid duplication in the case where two or morelines terminate at a bridging point, each ofl which Alines require, whentheyare transmitting into the amplifier, a connecting networklofthe-same characteristic. Instead of permanently associating an`individual network with each of these lines, a .single network havingthe proper characteristics is provided and arranged to be automaticallyswitched into the line transmitting into the amplifier, under control ofa key such as l431, .438, 439, 622, 623, etc., individual Ito the line.For example, if line 420from Philadelphia, and .from Albany, both ofwhich terminate at New York, are suciently alike in theircharacteristics so that `the respective attenuation equalizers 620 and126 are substantial equivalents, these networks can be omitted fromtheir respective lines and a single network 5|6, having lthe samecharacteristics, may be connected to the uppermost and lowermost frontcontacts of relay 5|0. When this arrangement is used, keys 121 and 623are permanently operated. Now in case the program is to be transmittedfrom Albany, control key 8|1 will be operated by the Albany attendantthereby causing relay 8|6 to operate and connect battery to the simplexcircuit over line 1|2 which causes relai7 '|06 at New York lto operate,which in turn operates relay 105. Operation of relay 106 will releaserelay 10| which in turn operates relay 102, Ythereby completing acircuit to hold relay |05 operated and to operate relays 502 and 509which latter relay operates due to the fact that with key 121 operated,resistance 128 is short-circuited and suflicient current now ows in theupper winding of relay 509 to overcome the non-operate bias on the lowerwinding. Relay 509 operates relay 5|0 in an obvious circuit which latterrelay closes its front contact thereby connecting the common network 5|6between the incoming line and the input of the amplifier which is theequivalent of providing the individual network 126 for line 1|2 which isconnected when relay 102 operates.

If the program is to be transmitted from Philadelphia the operation ofkey 4|1 will cause relay `604| to be operated and relay 603 to releaseand also to cause the operation of relay 608. The operation of relays604 and 608 completes a circuit to hold relay 608 operated and tooperate relay508. A-'s'key 623 is operated, relay 509 also soperateswhich in turn operates relay 5|0 and connects the network 5|6 betweenline '420 and vtheamplifier input.

As only one line is connected tothe amplifier -input-atthe same time,all'of thelines terminating at one switching -pointvand having the :samecharacteristics, #can :be .served by. one `common,

network thereby obviating `the unnecessary expense of providingindividual networks for each line.v

Relays 40|, 402-60I, 602-603, S04-10|', '|02- 103, 10d-80|, -802-803,804-805, 806-1 |0I, ||'02-| |03, IHM-|301, |302-I303, |304 and |305,|306 are for the purpose of `conditioning their respective lines withthe proper equipment for the direction in which the line istransmitting, i. e., into or away from the respective common amplifier360, 500, etc. For example, if a program is incoming over line l||9 fromthe south and west, which terminates in Philadelphia in the input ofamplifier 300, .the line requires the inclusion therein of anattenuation equalizer of certain characteristics which are predeterminedand suited to the characteristics of the line, whereas if the line 4|!!is connected to the output of amplifier 360 and is transmitting fromPhiladelphia to the south and west a transmission loss pad of the propercharacteristics is required, all of which will be understood by thoseskilled in the art.

As relays 40| and 402, etc., are controlled by current over simplexcircuits superimposed on the diierent lines, which lines are subject tovarious forms of interfering currents such as lighting, induced currentsfrom nearby power transmission lines, differences inV earth potential,etc., false operation of these relays `due to line surges is avoided bymaking them slow-acting, and by other delay circuits introduced, whenrequired, to suit the particular conditions.

At the diierent bridging points such as Philadelphia (Fig. 4), New York(Fig. 6), etc., where local broadcast lines terminate, the drawings showeither the studio microphone or the broadcast transmitter connected tothe network, but not both at the same time although it is evident thatusually a station originating a program in its studio will also desireto broadcast over its own antenna. In this connection the circuitarrangements shown by the drawing relate only to control of the. networkcircuit and it is assumed that local switching means will be employed toconnect the station transmitter Ato the network in case its studio isoriginating` a program an such a connection is desired.

What is claimed is:

1. In a two-way program transmission system, 4

a bridging station, a plurality of program lines terminating at saidbridging station, a ,program station at the other end of each line,program transmitting and receiving equipment at each program station,switching ymeans at each program `station normally connecting saidreceiving equipment to the line vand adapted when operated to disconnectsaid receiving equipment from the line and substitute said transmittinglequipment therefor, a common ampliiier having an input circuit and anoutput circuit at said .bridging station, switching means at thebridging station individual to each line normally connecting therespective lines to the output circuit and radapted when operated todisconnect the re-` spective lines from the output circuit and conneetthem to the input circuit, manually controlled means at each programstation `for operating the switching means thereat `to disconnect vthereceiving equipment and connect 'the trans- -mitting equipment and tooperate the respective switching means at the bridging station todisconnect the line from the .-amplier output and connect it to `theinput icircuit.

2.` In a .twofway l.program transmission system, .r

a bridging station, an amplifier at said bridging station having aninput circuit and an output circuit, a plurality of program stations,lines for each station normally connected in multiple l to the outputcircuit of said amplifier, relay means current, manually controlledswitching means at each program station for connecting one of saidsources to the respective simplex circuit, primary control meansassociated with each line at the repeater station responding to directcurrent incoming over the respective simplex circuit to repeat directcurrent to the primary control means at all other lines, said primarycontrol means being also responsive to direct current relayed thereto tore-relay direct currents to their respective simplex circuits, anamplifier at said repeater station having an input circuit and an outputcircuit, secondary relay means individual to each line normallyconnecting its respective line to the output circuit of said amplifierand responsive to operation of its respective primary control means inrepeating direct current incoming over the corresponding simplex circuitto transfer the respective line from the output circuit to the inputcircuit, and a pair of transmission correcting networks of differentcharacteristics asso ciated with each of certain of said lines, relaymeans associated with said certain lines controlled by the respectiveprimary control means for connecting one or the other of said networksin the line depending upon the direction said direct current is beingrelayed with respect to the line. 4. In a two-Way program transmissionsystem,

a plurality of program stations adapted to receive or transmit aprogram, a repeater station, a line from each program station to therepeater station, a simplex circuit from each program station to therepeater station comprising the conductors of the respective lines,sources of direct current, manually controlled switching means at eachprogram station for connecting one of said sources to the respectivesimplex circuit, primary control means associated with each line at therepeater station responsive to direct current incoming over therespective simplex circuit to repeat direct current to the primarycontrol means of all other lines, said primary control means being alsoresponsive to direct current relayed thereto to re-relay said directcurrents to their respective simplex circuits,` an amplier at saidrepeater station having an input and an output circuit, secondary relaymeans individual to each line normally connecting its respective line tothe output circuit of said amplifier and responsive to operation of itsrespective primary control means in repeating direct current incomingover the corresponding simplex circuit to transfer the respective linefrom the output circuit to the input circuit, a transmission correctingnetwork, means adapted when operated for connecting said network in theinput circuit of said amplier, and manually operated means, individualto said primary control means, for conditioning said network connectingmeans to operate when the primary control means, at whichthe manuallycontrolled means is operated, responds to direct current incoming overits associated line simplex circuit. ALBERT E. BACHELET. Y

